One of the major causes of atherosclerosis and coronary disease is attributed to high blood cholesterol levels. It has been estimated that at least about 50% of total body cholesterol is derived from de novo cholesterol synthesis. A major rate-limiting step in the cholesterol biosynthetic pathway is catalyzed by 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase. Compactin and pravastatin have been reported to be competitive inhibitors of HMG-CoA reductase, and the presence of either one can result in inhibition of cholesterol biosynthesis.
Microbial hydroxylation of compactin can produce hydroxylated forms of compactin, e.g., pravastatin. Some hydroxylated forms are reportedly more effective than compactin as competitive inhibitors of HMG-CoA. It has been reported that this hydroxylation can be effected to differing degrees by many different genera of fungi, and from the bacteria Nocardia and Streptomyces roseochromogenus and Streptomyces carbophilus. See, e.g., U.S. Pat. No. 5,179,013; U.S. Pat. No. 4,448,979; U.S. Pat. No. 4,346,227; U.S. Pat. No. 4,537,859; Canadian Patent No. 1,150,170; Canadian Patent No. 1,186,647; Serizawa et al., J. Antibiotics 36: 887-891 (1983).
A problem with using fungi for the production of pravastatin is that they generally do not tolerate increases in the amount of compactin added to the culture medium, presumably due to the anti-fungal activity of compactin. Serizawa et al., J. Antibiotics 36: 887-891 (1983).
The cytochrome P450 system has been shown to be required for the hydroxylation of compactin to pravastatin in Streptomyces carbophilus. Matsuoka et al., Eur. J. Biochem. 184: 707-713 (1989). Problems with the use of such an enzyme is that it is a complex of proteins rather than a single protein, making recombinant DNA manipulations difficult, and that compactin, which is an inducer of the cytochrome P450 system, is very expensive.